1. Field of the Invention
This invention relates to poly(alkylene terephthalate) polymers and more particularly to poly(alkylene terephthalate) polymers having stability at elevated temperatures.
2. Description of the Prior Art
Poly(alkylene terephthalate) polymers particularly poly(butylene terephthalate) and poly(ethylene terephthalate) are utilized in molding articles by thermoplastic molding techniques. In processing the poly(alkylene terephthalate) high temperatures are encountered in melting, extruding and forming the polymer which contributes to discoloration making the poly(alkylene terephthalate) molded articles unappropriate for the manufacture of articles which are to be color constant. Further, because of the heating necessary to process the polymer, the poly(alkylene terephthalate) undergoes molecular weight reduction causing a deterioration in the physical and mechanical properties of the molded article.
In the synthesis of poly(alkylene terephthalates) linear alkyl phosphites have been used to prevent discoloration of the polymer. The color stability problem during synthesis and the stability problem during processing present different problems to the corresponding manufacturers. The poly(alkylene terephthalate) is typically synthesized in an inert atmosphere and discoloration is due to the heat necessary to perform the esterification or transesterification of the monomers. Whereas during melt processing the polymer is subjected to both heat and air which has made the linear alkyl phosphites ineffective for stabilizing poly(alkylene terephthalates).
In accordance with the present invention poly(alkylene terephthalate) polymers are provided with improved resistance to color and molecular weight degradation during melt processing.